This application claims the priority of German application 197 41 869.4-21, filed Sep. 23, 1997, the disclosure of which is expressly incorporated by reference herein.
The invention relates to an arrangement for operating a brake of a vehicle having a controllable operating electric motor and a conversion device for converting the rotational movement of the operating electric motor into a translational movement of one or several braking elements operatively connected with the conversion device.
The increasingly dense road traffic requires systems which promote the driver's safety and contribute to relieving the driver. In the future, the driver of a motor vehicle will be aided by so-called "by-wire systems" and, in many driving situations, will be relieved by intelligent systems.
The predominant number of current brake systems consists of hydraulic or pneumatic transmission and booster devices by means of which the driver directly defines the brake intervention of the wheel brake. In order to control driver-independent brake interventions, such as a ranging control, in addition to the pressure supply required for this purpose, a plurality of components are required, such as valves, hydraulic cylinders and the like.
Electromechanical and electrohydraulic devices have also been suggested for operating a brake of a vehicle.
Such an arrangement is described, for example, in German Patent Document DE 42 29 042 A1. In the case of this arrangement, the operating electric motor is assigned to a brake element. The conversion device converts the rotational movement of the electric motor into a translational movement which results in a linear displacement of a driving piston. Between the driving piston and a brake lining contact pressure piston, by means of which the brake linings are brought against a brake disk, a fluid chamber is provided. A brake fluid is situated in the fluid chamber.
From German Patent Document DE 42 07 640 A1, a friction brake, particularly a disk brake, is known as well as a process for braking a vehicle which has an electromagnetic friction clutch which can be brought into a controllable frictional connection with a friction member, preferably a brake disk.
The friction clutch is in a form-locking rotating engagement by way of a pinion gear with a piston, which can be axially adjusted by a V-belt drive which is independent of the rotating direction, and which is part of an application device for brake linings assigned to the brake disk.
For pressing the brake linings against the brake disk, energy is taken from the rotating vehicle wheel by means of the friction clutch and is supplied to the application device.
One problem of such electromagnetic arrangements for operating a brake of a vehicle is its reliability. Thus, for example, self-locking transmissions are used for converting the rotational movement of the electric motor into a translational movement, which, for example, in the event of a failure of the brake during a short drastic braking, lead to a remaining of the brake in the operated condition, although the braking condition should have been terminated. This results in uncontrollable danger situations.
For this reason, in the case of German Patent Document E 42 29 042 A1, the contact pressure force generated by the electric motor is transmitted by way of a fluid chamber filled with brake fluid. By means of a pressure reduction in the brake fluid, the brake can be released in danger situations, for example, when the above-described transmission locking takes place. However, despite the electric controllability, this brake operating arrangement requires the use of a hydraulic system and therefore also of a brake fluid. It therefore requires not only high expenditures but, in particular, is also less friendly to the environment than a so-called "dry" brake which requires no hydraulic fluid.
Although in the case of the brake known from German Patent Document DE 42 07 640 A1, a self-locking is impossible, the problem and the disadvantage of this brake is the fact that the electromagnetic friction clutch itself is subjected to wear and therefore requires additional maintenance work on the brake which is connected with costs.
In the case of brakes of that type, there is also the problem that special electric motors as well as complicated transmissions are required for their operation, which reduce the reliability of such an electric brake and increase the manufacturing expenditures. Furthermore, such brakes do not meet or only very poorly meet the dynamics required for many applications, for example, for an antilock system or a wheel slip control system. In addition, such brakes require a relatively large installation space which is not available, particularly in a high-performance chassis.
Finally, the relatively high weight of such brake operating arrangement as an unsprung mass also has a negative influence on the dynamics of the chassis.
It is therefore an object of the invention to provide an arrangement for operating a brake of the initially mentioned type which, while its construction is compact, permits a very fast and reliable, also intermittent operation of a "dry" brake which can be controlled in a computer-assisted manner.
In the case of an arrangement for operating a brake of a vehicle of the initially described type, this object is achieved according to the invention in that at least one additional electric motor is provided which can be controlled separately of the operating electric motor and has at least one additional conversion device for converting the rotation of the at least one electric motor into a translational movement of the brake element(s) which is independent of the translational movement caused by the operating motor and its conversion device.
By means of the additional electric motor, which can be controlled separately of the operating electric motor and has another conversion device which causes a conversion of the rotation of this electric motor into a translational movement of the brake element(s), which is independent of the translational movement caused by the operating electric motor, a release of the brake is permitted not only in any position, but also particularly in the event of a failure of the operating electric motor. As a result, an adjusting of the brake elements and thus of the brake lining for a braking of the parking brake, a fast approaching of the brake elements and thus of the brake linings for overcoming the lifting play,as well as a readjusting of the brake in the case of a wear of the brake lining, can be implemented.
As a result, a faster response of the brake is permitted and, in a particularly advantageous manner, the above-described danger situation, which is caused by a faulty operating of the brake, is avoided.
In order to increase particularly the safety of the brake, it is advantageously provided that the operating electric motor and the at least one additional electric motor have mutually separate electric circuits. As a result, it is avoided that, for example, in the event of a failure of the electric circuit of the operating electric motor,the whole brake fails since the adjusting as well as the returning of the brake is permitted by the additional electric motor and the conversion device assigned to it.
In order to permit particularly a parking brake function, it is advantageously provided that the braking element(s) can be blocked by means of the at least one additional electric motor and its conversion device. As a result, any additional parking brake devices can be eliminated on the arrangement for the operation of the brake.
It is also preferably provided that, by means of the at least one additional electric motor and its conversion device, the brake element(s) can be reset in the event of a failure of the operating motor. This effectively avoids danger situations which arise because of a failure of the operating motor.
Details of the construction and the arrangement of the electric motors and of the conversion devices has not been set forth above. Advantageously, it is provided that the conversion devices are part of a housing on which the operating electric motor as well as the additional electric motor(s) are fastened. This permits not only a compact and space-saving constructional shape but also a modular construction which, in particular, permits a simple exchangeability of the electric motors, a good access to the electric motors and, on the whole, a simple construction of the whole arrangement.
The analyzability of the electric motors also provides a diagnostic capability of the system, for example, within the scope of an on-board diagnosis.
As far as the arrangement of the operating electric motor and the conversion unit assigned to it is concerned, various embodiments are contemplated.
A particularly advantageous embodiment., which includes a compact construction, provides that the operating electric motor is arranged axially with respect to the brake element(s), and the conversion unit assigned to it comprises an axially arranged step-down transmission by means of which the brake element(s) can be operated by means of an adjusting device which causes an axial displacement of an adjusting piston.
As the result of the coaxial construction of the brake element, the operating electric motor and the step-down transmission, a particularly a simple and compact construction is permitted which, in addition, requires only a few component parts.
Advantageously, the step-down gear is a harmonic drive transmission.
As far as the arrangement of the at least one additional electric motor and the construction of the conversion unit assigned to it is concerned, it is advantageously provided that the at least one additional electric motor is arranged parallel to the axis of the operating electric motor, and the conversion device assigned to it is a transmission which operates the adjusting device. As the result of the fact that the at least one additional electric motor by way of the transmission assigned to it is in an engagement with the adjusting device, which transmission can, on the other hand, also be operated by the operating electric motor, in a particularly simple manner, an operation of the arrangement is permitted by means of two electric motors which both cause an operation of the brake elements.
In this case, the transmission is preferably a spur gear which permits an extremely compact construction.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.